Late-stage Deformation Research Articles

In-situ study of tensile behavior of Ti/Al laminated metal composites fabricated via ultrasonic additive manufacturing

In this paper, the in-situ tensile behavior of Ti/Al laminated metal composites (LMCs) prepared via ultrasonic additive manufacturing (UAM) was investigated by optical microscopy combined with digital image correlation. Compared with pure Ti foil and Al/Al LMCs processed via UAM, the Ti/Al LMCs exhibit a significantly larger plasticity with intermediate tensile strength. This can be attributed to (ⅰ) strain dispersion in Ti/Al LMCs, (ⅱ) necking inhibiting due to well-bonded interface during early stage of deformation, and (ⅲ) microcracking during late stage of deformation at the rough Ti/Al interfaces, which originate from direct contact between Ti foil and sonotrode.

Effect of strain state on the surface roughening for hydroforming of aluminum alloy tube based on cross-scale numerical modeling

The complex deformation behavior would result in surface roughening such as orange peel defect during the hydroforming process of aluminum alloy tubular parts. In order to control the surface quality of hydroformed tubular parts, the effect of strain state on the surface roughening for 2219 aluminum alloy tube was analyzed based on a cross-scale model. The model combined the crystal plasticity model and macroscopic finite element model. During the uniaxial tension, the surface morphology reveals an equiaxed pattern characteristic of orange peel due to the strain incompatibilities between grains, and the peak and valley are stretched along the tensile direction. The surface roughness under tension-compression plane strain state is the lowest due to the low through-thickness strain. In the biaxial tension region, the change rate of surface roughness gradually increases with the decrease of the second principal strain especially in the late deformation stage, and the surface features evolve from an orange peel pattern to a ridging pattern. The forming limit diagram under different strain states based on surface roughness was established to guide the optimization of hydroforming process. Compared with the one-step hydroforming, the surface roughness of the bulging peak of 2219 aluminum alloy tube using multi-step hydroforming with the axial self-feeding decreases obviously from 16.3 to 10.8 μm due to the significant reduction of the equivalent strain.

Strength Weakening and Phase Transition Mechanisms in Nanoindentation of Al/Mg-Layered Nanocomposites: A Molecular Dynamic Study

Molecular dynamics (MD) simulations were performed to investigate the nanoindentation behavior of Al/Mg-layered nanocomposites with varying layer thicknesses and Mg layer orientations in this study. The aim is to understand the weakening mechanisms at low layer thicknesses and the phase transition mechanisms associated with the dislocation slip angle in the Mg layer. Results indicate that the nanoindentation strength of nanocomposites increases with the layer thickness in the range of 1–10 nm, with the strength of 9.5 × 10−7 N at 10 nm being approximately 73% higher than that at 1 nm. This strength increase is mainly attributed to high interfacial stress, the higher percentage of amorphous atoms, weakened interatomic interactions, and the transition of adjacent interfaces to fully coherent interfaces that significantly reduce their ability to hinder dislocations at the low-layer thickness range. Additionally, in the initial deformation process, the hexagonal close-packed (HCP) phase of the Mg layer firstly transforms into the body-centered cubic (BCC) phase due to its lower energy barrier, followed by the emergence of a faced-centered cubic (FCC) phase driven by 1/3<1−100> dislocations. In the late stage of deformation, new dislocations are generated in the FCC phase and move along its slip planes, altering the dislocation direction. The FCC/HCP interfacial configuration also affects the HCP phase transition mechanism in the Mg layer. When the dislocation slip angle is 0°, the primary phase transition is the BCC phase, whereas a 45° slip angle results in the FCC phase. These findings will provide a guide for the preparation and manufacturing of new high-quality layered nanocomposites.

Achieved strength-plastic trade-off in HfMoNbTaTi refractory high-entropy alloy via powder metallurgy process

The practical application of refractory high-entropy alloys (RHEAs) has been limited by their brittleness at room temperature. This study prepared fine-grained HfMoNbTaTi refractory high-entropy alloys using a powder metallurgy process combining mechanical alloying (MA) and spark plasma sintering (SPS). This method effectively addresses the issue of room temperature brittleness and achieves a favorable balance between strength and plasticity. The resulting sintered alloy comprises two body-centered cubic (BCC) solid solution matrices and a range of nanoprecipitates, including the γ-phase, σ-phase, and α-phase. With increasing sintering temperature, the average grain size increased from 0.45 μm (at 1400 °C) to 4.56 μm (at 1700 °C). Simultaneously, the content of the γ-phase gradually decreases due to the greater influence of mixing entropy. Under quasi-static loading, the fine-grained multiphase structure not only benefits from grain boundary strengthening and precipitation strengthening effects, but also enhances the deformation uniformity, ultimately improving both the strength and plasticity. At 1450 °C, the sintered alloy exhibited a compressive yield strength of 2325 ± 8.40 MPa and a plastic strain of 26.44 ± 1.17 %. These values represent a 35.73 % increase in yield strength and a 120.33 % increase in plastic strain compared to those of the as-cast alloy. The deformation process at room temperature is mainly governed by the multiplication of screw dislocations and cross-slips. In the middle and late stages of deformation, the grains exhibit a preferred orientation, further enhancing the plastic strain. In summary, this study presents a practical approach for overcoming the issue of room temperature embrittlement in RHEAs.

Evolution of deformation structures in CrCoNiSi0.3 medium entropy alloy subjected to high-strain-rate and quasi-static compressive deformation

The objective of the present study is to fundamentally explore the evolution of deformed structures of CrCoNiSi0.3 medium entropy alloy subjected to high-speed compression deformation with true strains of 0.16, 0.33, and 0.46 (via split Hopkinson pressure bar system, strain rate of ∼6 × 103 s−1, denoted as HSR deformation), and quasi-static compression deformation with true strains of 0.20, 0.30 and 0.50 (via MTS compression system, strain rate of ∼10−3 s−1, denoted as LSR deformation). From the comparison between the results of HSR and LSR samples, it clearly indicates that the formation of deformation nanotwins is promoted under the HSR deformation and enhances the work hardening effect in the early stage of deformation; as the HSR deformation proceeds, the nanotwins effectively provide the dynamic Hall–Petch effect, leading to an increase in flow stress beyond the stress required for HCP phase transformation. The HCP phase also induces a stronger work hardening capacity at the late stage of deformation. Profuse deformation nanotwins and HCP phase promoted by HSR deformation result in a strong work hardening effect. Furthermore, the flow stress of the HSR deformed sample with a true strain of 0.46 is 1536 MPa, which is about 36% higher than that of the LSR deformed sample with the same true strain, 1102 MPa. It is clear that under the HSR deformation, the defect structures including deformation nanotwins and ultra-thin HCP platelets are much more favorably generated, greatly improving the working capacity.

1.88 Ga granitoids at Sorsakoski, Central Finland: A-type magmatism within the Raahe-Ladoga suture zone

Four quartz monzonite – granite intrusions forming the Sorsakoski granite lithodeme, are found within the Raahe-Ladoga suture zone in Central Finland. The prevailing potassium feldspar megacrystic quartz monzonites and granites form a bimodal association with diorites and gabbros. The granitoids are mainly calc-alkaline, ferroan, per- to metaluminous, and have high Zr and REE contents. Dominant mafic minerals are biotite and hornblende, clinopyroxene and orthopyroxene are locally present. The mafic units display effects of fractionation of clinopyroxene. In our interpretation, these intrusions were emplaced during regional late stages of deformation and post-crystallisation deformation partitioned into major shear zones leaving bulk of the intrusions relatively undeformed. Based on one new (1876 ± 6 Ma) and one pre-existing (1882 ± 5 Ma) U-Pb zircon age determination, the crystallisation age of the granitoids can be assumed at ca. 1880 Ma. Based on mineralogy, petrography, geochemistry, bimodal nature of magmatism and age, we correlate these intrusions to the A-type rocks of the previously described Saarijärvi suite. This shows that the syn-orogenic A-type magmatism extended eastwards beyond the Central Finland Granitoid Complex.

Cold deformation behavior and microstructure evolution of biomedical Cu-containing L605 alloy

The effect of copper (Cu) addition on the microstructure evolution and deformation mechanism of L605 (Co-20Cr-15 W-10Ni) alloy during cold deformation was investigated by using transmission electron microscopy (TEM), X-Ray diffraction (XRD) and electron backscatter diffraction (EBSD) analysis. The results indicated that the addition of Cu slightly decreased the yield strength and ultimate tensile strength, while it significantly increased the elongation. EBSD results revealed that hexagonal close-packed (HCP) martensite was generated during cold deformation and increased with increasing cold deformation level. The deformation microstructure of both alloys at different cold deformation levels shows that the stacking faulting was the primary deformation mechanism at early stage of cold deformation, in contrast, dislocation planar-slip and face-centered cubic (FCC) to HCP martensitic transformation were prevailed at both medium and late cold deformation level. Cu addition significantly suppressed the dislocation and stacking fault multiplication at early deformation stage and delayed the martensitic transformation at medium and late deformation stage, which could be ascribed to the relatively high stacking faulting energy by Cu addition, resulting in the low strain hardening behavior in the entire deformation process. These cumulative results and analyses could provide a solid foundation for the further development of this novel type of biomedical Cu-containing cobalt-based alloy.

Achieving prominent high-temperature mechanical properties in a dual-phase high-entropy alloy: A synergy of deformation-induced twinning and martensite transformation

Dual-phase high-entropy alloys are renowned for their favorable balance of strength and ductility at ambient conditions. However, their mechanical properties, especially the associated deformation mechanisms at elevated temperatures, remain less explored. In this study, the AlCoCrFeTi0.5Ni2.5 HEA consisting of FCC (i.e., L12) and BCC (i.e., B2 + A2) phases was subjected to compressive test at elevated temperatures ranging from 500 to 800 °C. The results demonstrate that this HEA exhibits excellent high-temperature mechanical properties up to 700 °C, superior to most refractory HEAs and Inconel 718 superalloy. Notably, its yield strength surpasses 1000 MPa, with pronounced strain-hardening evident at 600 °C. Upon reaching 700 °C, despite strain-softening occurring at the late deformation stage, the yield strength remains above 900 MPa. Microstructural analysis of the sample deformed at 600 °C indicates increased stacking faults and deformation twins in the FCC phase. Additionally, the BCC phase displays a high density of dislocation entanglements and nanoscale martensite lathes. It is revealed that the high-temperature twins in the FCC phase are triggered by the pre-existing local chemical ordered domains, while the martensitic laths in the BCC phase are activated via stress-induced phase transformation driven by stress concentration at the B2/A2 interface. The synergistic effect of multiple deformation mechanisms operating in both the FCC and BCC phases significantly enhances the strain-hardening capability, contributing to the remarkable mechanical properties at elevated temperatures. These findings provide valuable insights for developing dual-phase HEAs with outstanding mechanical properties over an extensive range of temperatures.

Two phases of Cretaceous dextral shearing recorded in the plutonic rocks of NW Nevada (USA): A tectonic link between intra-arc shearing in the Sierra Nevada and Idaho batholiths

Abstract The Cretaceous intrusive units of the Sahwave and Nightingale ranges in northwestern Nevada, USA, located between the Sierra Nevada and Idaho batholiths, represent a critical segment of Cretaceous arc magmatism. U-Pb zircon age dating shows that the older, 104 Ma Power Line intrusive complex is dominantly granodioritic in composition, while the younger 94–88 Ma Sahwave Range intrusive suite (the Juniper Pass, Bob Springs, and Sahwave plutons) is similar in composition (tonalite to granodiorite) and age to the plutons of the Tuolumne intrusive suite of the east-central Sierra Nevada batholith. We present new field measurements, microstructural observations, and anisotropy of magnetic susceptibility analyses of the Power Line intrusive complex and Sahwave Range intrusive suite. The Power Line intrusive complex is characterized by a vertical, N–S-striking, solid-state foliation and down-dip lineation. Evidence of dextral shearing is observed on subhorizontal planes that are perpendicular to the lineation, which is consistent with pure shear-dominated transpression. This fabric is similar in style and timing to both the western Idaho shear zone of the Idaho batholith and mid-Cretaceous shear zones of the central Sierra Nevada. The plutons of the Sahwave Range intrusive suite are not affected by the pure shear-dominated transpressional fabric observed in the Power Line intrusive complex, which indicates that this deformation ceased by ca. 94 Ma. Rather, the Juniper Pass pluton contains an E–W-striking magmatic foliation fabric that rotates to a steep NW–SE-striking, solid-state foliation in the younger Sahwave pluton. These fabrics are strikingly similar to fabrics in the Tuolumne intrusive suite, Sierra Nevada, California, USA. Recent work in the western Idaho shear zone also indicates that late-stage deformation occurred there until ca. 85 Ma. Therefore, the intrusions of northwestern Nevada provide a tectonic link between the Sierra Nevada and Idaho batholiths, which suggests that two distinct phases of mid-Cretaceous, transpressional deformation occurred in at least three magmatic arc segments of the western U.S. margin.

Lattice preferred orientation of quartz in granitic gneisses from Tso Morari Crystalline Complex, Eastern Ladakh, trans-Himalaya: evaluating effect of Dauphiné twin in dynamic recrystallization during exhumation

Abstract The Tso Morari Crystalline complex (TMCC) of eastern Ladakh, India, is part of the north Indian continental margin and is characterized by eclogitic enclaves embedded within ortho- and paragneisses known as the Puga Gneiss. Two fault zones bound the TMCC: the Karzok fault to the southwest and the Zildat fault to the northeast. In the present study, we carried out Electron Backscatter Diffraction study of quartz of 10 samples collected from the Puga Gneiss. The relict and recrystallized quartz grains were treated separately to understand the deformation conditions of the Puga Gneiss during early and late deformation stages related to UHP metamorphism and final stage of exhumation during retrogression, respectively. Microstructural observations suggest dynamic recrystallization in quartz and plagioclase at different temperature ranges. Misorientation analysis of both relict and recrystallized quartz grains reveals presence of Dauphiné Twins. Lattice preferred Orientation (LPO) of <c> axis of relict quartz grains generally shows more than one point maxima indicating that the relict grains preserve LPO developed during different stages of metamorphism/deformation. On the other hand, LPO of <c> axis of recrystallized grains from Karzok and Zildat fault zones shows asymmetric single girdle either normal or at an angle to the foliation plane, which suggests simple shear. We conclude that grain size reduction and recrystallization of the Puga Gneiss was greatly influenced by Dauphiné Twin and the final exhumation of the TMCC took place in a simple shear environment aided by activity along its two binding fault zones.

Dual-interstitials promoted multiple mechanisms enhance strength-ductility synergy of an equiatomic high-entropy alloy

Although minor additions of interstitials have been employed to enhance the yield strength of high-entropy alloys (HEAs) with multi-principal elements, the significant loss of ductility occurs as the cost. In this work, to further improve strength-ductility synergy of the model face-centered cubic (FCC) CoCrFeMnNi HEA, dual-interstitial alloying of C and N is manipulated with the emphasis on tuning the microstructures and multiple strengthening mechanisms. C (0.6 at%) and N (0.8 at%) are completely dissolved in the FCC matrix after annealing at or above 1150 °C. The dissolution of the dual-interstitials in the matrix refines grains by impeding grain boundary migration via solute atmospheres. Nanoprecipitates including M23C6, Cr3C2 and Cr2(N, C) are dispersed in the recrystallized FCC matrix of the dual-interstitial HEAs upon annealing at 950–1000 °C. The Zener pinning pressure induced by these nanoprecipitates retards grain boundary migration and hence reduces grain sizes. The primary deformation mechanism is dislocation slip in both dual-interstitial HEAs with and without precipitates at the early deformation stages (e.g., 40% local strain), the mechanical twinning occurs at the medium and late deformation stages (e.g., 60% and 90% local strains, respectively) contributing to the high ductility of the HEAs. The synergetic strengthening effects of nanoprecipitates, grain boundaries, interstitial and substitutional solid-solution brings about high yield strength of 772 MPa and ultimate tensile strength of 1178 MPa at a large elongation of 34% in the dual-interstitial HEA containing carbides/carbonitrides nanoprecipitates. The contributions of the multiple mechanisms are quantified and discussed.

Elucidating the evolution of long-period stacking ordered phase and its effect on deformation behavior in the as-cast Mg-6Gd-1Zn-0.6Zr alloy

Herein, the evolution of long-period stacking ordered (LPSO) phases in the as-cast Mg-6Gd-1Zn-0.6Zr (wt.%) alloy are investigated via transmission electron microscopy (TEM) and atom probe tomography (APT). The TEM results reveal that two types of LPSO phase (a bulky interdendritic phase and a plate-like matrix LPSO phase) are formed in the as-cast sample. Most of the LPSO phases are confirmed to be of the 14H type, with a smaller proportion being of the 18R LPSO. Further, the APT results reveal that the composition of the interdendritic LPSO phase is closer to that of the ideal 14H phase compared to the matrix LPSO phase, and both the interdendritic and matrix LPSO phases exhibit a Gd/Zn ratio of 2.5, thereby indicating a deficient Zn content compared to the ideal 14H phase (i.e., 1.3). In addition, the influence of the LPSO phases on the deformation behavior is investigated at different compressive plastic strains using electron backscatter diffraction (EBSD) analysis to reveal twinning and slip behavior during deformation. The results indicate that the LPSO phase induces additional work hardening in the late stage of deformation via the suppression of {101¯1} compressive twinning and the activation of non-basal slip systems.

Microstructure Evolution and Deformation Behavior of Extruded Mg-5Al-0.6Sc Alloy during Room and Elevated Temperature Tension Revealed by Ex-Situ EBSD and VPSC.

In this study, the microstructure evolution and deformation behavior of the extruded Mg-5Al-0.6Sc (AS51) alloy during tensile testing at room temperature (RT) and 250 °C were investigated by electron backscattered diffraction (EBSD) characterization and Visco Plastic Self Consistent (VPSC) simulation. The results showed that a continuous hardening behavior of the alloy occurred during the deformation at RT, and a certain softening was caused by the occurrence of dynamic recovery (DRV) and dynamic recrystallization (DRX) in the late stage of deformation at 250 °C. The primary deformation mechanism at both RT and 250 °C was dislocation slip, with prismatic <a> slip being the dominant deformation mode, and no significant changes in grain size or texture type occurred. By identifying the activated twin variants, the results indicated that the selection of twin variants was closely related to the local stress concentration. The relatively low activation frequency of extension twinning at 250 °C is partly attributed to the fact that the consumption of dislocations by DRV and DRX can effectively relax the local stress concentration. Meanwhile, the DRX mechanism during the deformation of the alloy at 250 °C was mainly discontinuous dynamic recrystallization (DDRX), with a low recrystallization fraction.

Role of prismaticdislocations in sub-zero temperature deformation of Mg-Gd-Y-Zr alloy

This work investigates the effect of activating and accumulating prismatic<a>dislocations on ductility of a Mg-7.37Gd-3.1Y-0.27Zr (GW83K) alloy at sub-zero temperatures. It is found that the prismatic <a> dislocations were more easily activated with decreasing temperature due to the lowering of CRSS prismatic<a>/CRSS basal<a> ratio in this alloy. Increasing the proportion of prismatic<a>dislocations shows limited effect on improving the ductility of GW83K alloy in the early-stage deformation at sub-zero temperatures, because the prismatic<a>dislocations cannot accommodate c-axis deformation. However, with the formation of low-angle grain boundaries rotating along [0001] axis induced by the accumulation of prismatic<a>dislocations, the GW83K alloy can perform a much better ductility in the late-stage deformation. Such a finding provides a new perspective on understanding the contribution of prismatic <a>dislocations to ductility in Mg alloys.

A novel dual-heterogeneous-structure ultralight steel with high strength and large ductility

A dual-heterogeneous structure with bimodal grain size distributions of both austenite and B2 phase was developed in a novel ultralight steel by a simple rolling and annealing process. Tensile test results show that the steel annealed at 900 °C (denoted as A900) exhibited the superb synergy of a high specific yield strength of 160.3 MPa g cm−3, a high tensile strength of 1300 MPa, a large ductility of 39.3% and a persistently high work hardening rate, which can be mainly attributed to the heterogeneous structures caused multi-level deformation mechanisms. Detailed microstructural analysis of the deformed A900 samples unveils that with an increase of strain, the plastic deformation of individual austenite grains was governed by different factors, i.e., grain size and Schmid factor (SF) at 4.2% and 9% strains and local stress at 25% strain, while the deformation of individual B2 grains was mainly regulated by grain size at 4.2%, grain size and SF at 9% strain and local stress in the late deformation stage, which leads to the consistently high work hardening rate and large elongation. In addition, owing to the hardness difference, a high density of geometrically necessary dislocations was observed near the interfaces of austenite/B2, which also contribute to the consistently high heterogeneous deformation-induced strengthening effect and thus the outstanding mechanical properties. The present work sheds light on the dual-heterogeneous structure of the ultralight steel that can be feasibly employed, and it could guide the optimization of mechanical performance of a wide range of alloys for lightweight engineering.

Mapping Structurally Controlled Alterations Sparked by Hydrothermal Activity in the Fatira–Abu Zawal Area, Eastern Desert, Egypt

AbstractThe Eastern Desert of Egypt suffered a protracted period of deformation triggered by cratonization of the new juvenile crust known as the Arabian Nubian Shield (ANS), which has been proposed for potential gold discoveries associated with the corresponding tectonic event. The Fatira area, on the border of Egypt's Northern and Central Eastern Deserts, is covered with metavolcanic rocks twisted by a dextral relocation of the Fatira Shear Zone (FSZ) relative to the Barud magmatic body. The recent study evaluated many deformed post‐orogenic granitic intrusions and felsite dikes associated with promising mineralization localities, notably orogenic gold deposits. The combination of various field observations and remote sensing data, followed by the analysis of aeromagnetic enhanced maps, allowed the differentiation of distinct lithologies, structural features, and hydrothermal alterations in the study area. Additionally, the integrated results obtained from the different interpretation techniques are utilized to identify and confirm the previously supposed mineralized localities in the Fatira and Abu Zawal areas and predict other matched localities. The final ASTER, Sentinel 2 hydrothermal alteration, and orientation entropy heat maps demonstrate the association between these mineralized regions and major structures related to the FSZ late stage of deformation rather than other structures studied throughout the area of interest.

Effect of tempering and partitioning (T&P) treatment on microstructure and mechanical properties of a low-carbon low-alloy quenched and dynamically partitioned (Q-DP) steel

We performed a direct quenching and dynamical partitioning (Q-DP) process, following intercritical annealing, to a low-carbon low-alloy steel. Performing an additional tempering treatment on the Q-DP steel, we investigated the carbon partitioning behavior upon tempering. We emphatically analyzed the effect of tempering and partitioning (T&P) treatment on the microstructure evolution and mechanical properties of the Q-DP steel, especially on carbon partition, retained austenite stabilization, TRIP effect and work hardening. Results show that the synergetic partition of carbon and Mn from ferrite to austenite during intercritical annealing and the dynamical partition of carbon upon quenching jointly achieve the stabilization of retained austenite in the Q-DP sample. The actual volume fraction of retained austenite is larger than the theoretical calculating value, which is attributed to the dynamical partition of carbon. The T&P treatment at 300 °C for 15 min does not result in obvious decomposition of retained austenite, but leads to apparent carbon partition from martensite to retained austenite. The carbon partition upon tempering enhances the mechanical stability of retained austenite, thus weakening the TRIP effect during tensile deformation and promoting the TRIP effect to occur at higher true strain level. The much higher work hardening rate at the late deformation stage near necking, for the quenched tempered and partitioned (Q-T&P) sample, leads to a higher uniform elongation, compared with the Q-DP sample. The existence of carbon-enriched stable retained austenite after necking happens finally enhances the post necking elongation of the steel.

The contribution of retained martensite to the high yield strength and sustainable strain hardening of a hierarchical metastable austenitic stainless steel

A hierarchical metastable austenitic stainless steel (ASS) is obtained through severe asymmetric cold rolling (about 92% reduction) and reversion annealing. The microstructure evolution and tensile deformation behavior were studied to clarify the effect of hierarchical microstructure including reversed austenite with different grain size and retained martensite on the mechanical properties and strain hardening behavior. The results show that a hierarchical multiphase structure including austenite with a bimodal structure and retained martensite is achieved after annealing at 700 °C, and this sample has a good combination of desirable strength and ductility (the yield strength (YS), the ultimate tensile strength (UTS) and the total elongation (TE) were 823 MPa, 916 MPa and 43.82%, respectively). The introduction of retained martensite can not only enhance the YS, but also promote martensitic transformation of the surrounding nano grains (NGs) at large strains. Therefore, the hierarchical TRIP effect, which occurred firstly in the fine grains (FGs) in the early deformation stage and then in the NGs in the late deformation stage, contributes to the good ductility. Meanwhile, the multiplication of high dislocation density and the ultrafine ε martensite contribute to the high work hardening.

Some Like It Cold: The “Conundrum of Samail” Revisited

AbstractMost tectonic models consider that the “Samail subduction zone” was the only subduction zone at the mid‐Cretaceous convergent Arabian margin. We report four new Rb‐Sr multimineral isochron ages from high‐pressure (HP) rocks and a major shear zone of the uppermost Ruwi‐Yiti Unit of the Saih Hatat window in the Oman Mountains of NE Arabia. These ages demand a reassessment of the intraoceanic suprasubduction‐zone evolution that formed the Samail Ophiolite and its metamorphic sole in the Samail subduction zone. Our new ages constrain waning HP metamorphism of the Ruwi subunit at ∼99‐96 Ma and associated deformation in the Yenkit shear zone between ∼104 and 93 Ma. Our ages for late stages of deformation and HP metamorphism (thermal gradients of ∼8–10°C km−1) overlap with published ages of ∼105‐102 Ma for Samail‐subduction‐zone prograde‐to‐peak metamorphism (thermal gradients of ∼20–25°C km−1), subsequent decompressional partial melting of the metamorphic sole and suprasubduction‐zone crystallization of the Samail Ophiolite (thermal gradients of ∼30°C km−1) between ∼100 and 93 Ma. Thermal considerations demand that two subduction zones existed at the mid‐Cretaceous Arabian margin. High‐pressure metamorphism of the Ruwi‐Yiti rocks occurred in a mature, thermally equilibrated “Ruwi subduction zone” that formed at ∼110 Ma. Initiation of the infant, thermally unequilibrated and, thus, immature, outboard intraoceanic Samail subduction zone occurred at ∼105 Ma. The Samail Ophiolite and its metamorphic sole were then thrust over the exhuming Ruwi‐Yiti HP rocks and onto the Arabian margin after ∼92 Ma, while the bulk of the Saih Hatat HP rocks below the Ruwi‐Yiti Unit started to be underthrust in the Ruwi subduction zone.

On the micromechanism of superior strength and ductility synergy in a heterostructured Mg-2.77Y alloy

Heterostructured metals and alloys are a new class of materials in which mechanical behaviors between the heterogeneous regions are significantly different, and the mechanical properties of bulk materials are superior to the superposition of individual regions. In this paper, three distinct types of heterostructures were constructed in Mg-2.77Y (wt.%) alloy by applying simple thermomechanical processing. Namely, Type I: the non-recrystallized grains of several tens of microns were embedded in the micron-scaled recrystallized grains that were distributed along shear bands and dispersed near grain boundaries; Type II: the aggregations of micron-scaled recrystallized grains were surrounded by the non-recrystallized grains; Type II: the micron-scaled recrystallized grains dominated the microstructure, and the non-recrystallized regions with diameters of tens of micrometers were surrounded by those fine recrystallized grains. Mechanical tests showed that the material with type III heterostructure had the optimal combination of yield strength and uniform elongation. This is attributed to its remarkable hetero-deformation induced (HDI) strengthening and dislocation strengthening. At the initial stage of plastic deformation (engineering strain below 4%), the rapid accumulation of geometrically necessary dislocations (GNDs) at the interfaces between recrystallized and non-recrystallized regions and between neighboring recrystallized grains lead to the significant HDI strengthening. As deformation proceeded, the HDI strengthening effect gradually decreased, and the traditional dislocation strengthening that was caused by GNDs accumulation at grain boundaries became significant. In-situ electron back-scattered diffraction (EBSD) testing revealed that the non-basal slip in the non-recrystallized regions became more remarkable in the late stage of deformation, which improved ductility and strain hardening of the alloy. These findings provide new insight into the design of high-performance hexagonal close-packed structural materials by using the concept of HDI strengthening.